Stacked die assembly

ABSTRACT

A sensor device comprising: a lead frame; a first/second semiconductor die having a first/second sensor structure at a first/second sensor location, and a plurality of first/second bond pads electrically connected to the lead frame; the semiconductor dies having a square or rectangular shape with a geometric center; the sensor locations are offset from the geometrical centers; the second die is stacked on top of the first die, and is rotated by a non-zero angle and optionally also offset or shifted with respect to the first die, such that a perpendicular projection of the first and second sensor location coincide.

FIELD OF THE INVENTION

The present invention relates to the field of sensor devices, and morein particular to a sensor device for use in an automotive environment,the sensor device comprising two semiconductor dies, one for performingan actual measurement and one for performing a redundant measurement.

BACKGROUND OF THE INVENTION

Sensor devices with high reliability are important in a wide variety ofapplications, such as for example, in automotive applications.Furthermore, it is often preferred to include a plurality ofsubstantially identical sensors, e.g. two sensors, in order to provideredundancy, e.g. in applications that are critical for ensuring safety.

Redundant sensor devices are known in the art, in which a plurality ofsubstrates that each comprise at least one sensor are combined in asingle package to provide an actual sensor measurement and a redundantsensor measurement. Devices in which two substrates are placed side byside require a larger footprint, which is undesirable. In order todecrease the footprint, the substrates can be stacked on top of eachother, for example as shown in FIG. 1 to FIG. 3 , each solution havingits advantages and disadvantages, for example in terms of packagefootprint, package thickness, measurement accuracy, component count,complexity of the production process, etc.

There is always room for improvements or alternatives.

SUMMARY OF THE INVENTION

It is an object of embodiments of the present invention to provide asensor device comprising two stacked substrates each comprising a sensorstructure, in particular a magnetic sensor structure and a magneticsensor system comprising same.

It is an object of embodiments of the present invention to provide sucha sensor device and a sensor system for use in an automotiveenvironment, to perform an actual measurement and a redundantmeasurement, for example for improving safety.

It is an object of embodiments of the present invention to provide sucha sensor device in a compact package, for example having a relativelysmall or reduced package footprint, and/or a relatively small or reducedpackage height.

It is an object of embodiments of the present invention to provide sucha sensor device where the measurement results (e.g. the measured signalsor values derived therefrom) are better matched, and/or which is easy oreasier to produce or assemble (e.g. easier to electrically connect to alead-frame, e.g. easier to wire-bond).

It is an object of particular embodiments of the present invention toprovide such a sensor device where the two sensor structures aremagnetic sensor structures.

It is an object of particular embodiments of the present invention thatthe sensor device can have two similar or identical substrates, while atthe same time providing measurement results which are better matched,and which is easy or easier to produce or assemble.

It is an object of particular embodiments of the present invention toprovide a magnetic sensor device or system, which moreover is highlyinsensitive to an external disturbance field.

These and other objectives can be achieved by a device and a methodaccording to embodiments of the present invention.

According to a first aspect, the present invention provides a sensordevice comprising: a lead frame; a first semiconductor die having afirst rectangular shape with a first geometrical center (6 a), and beingelectrically connected to the lead frame, and comprising a first sensorstructure situated at a first sensor location; a second semiconductordie having a second rectangular shape equal to the first rectangularshape, and having a second geometrical center (6 a), and beingelectrically connected to the lead frame, and comprising a second sensorstructure situated at a second sensor location; wherein the first sensorlocation is offset from the first geometrical center; the second sensorlocation is offset from the second geometrical center; the secondsemiconductor die is stacked on top of the first semiconductor die, andis rotated and optionally also shifted with respect to the firstsemiconductor die such that an orthogonal projection of the first andthe second sensor location onto the lead frame coincide.

The “sensor structure” comprises one or more “sensitive elements”.

For example, in case of a “magnetic sensor device”, each sensorstructure comprises one or more magnetic sensitive elements, and mayfurther comprise for example an integrated magnetic concentrator (IMC).The magnetic sensitive elements may for example be chosen from the groupconsisting of: horizontal Hall elements, vertical Hall elements,magneto-resistive elements (such as e.g. AMR, GMR, TMR elements).

The “first sensor structure” is located at a “first sensor location”,which can be defined as a point located substantially “in the middle”of, or in the middle between the one or more sensitive elements.

Preferably the rotation is a rotation about an axis perpendicular to thelead frame.

Preferably the first and the second semiconductor die are located on thesame side of the lead frame and oriented such that their active surfacesare oriented in the same direction (e.g. both away from the lead frame).

Preferably the relative position L1 of the first sensor location withrespect to the first rectangular shape is identical to the relativeposition of the second sensor location with respect to the secondrectangular shape.

It is a major advantage of this magnetic sensor device that theelectrical connections can be performed on the top side, in a simplemanner, using standard equipment, contrary for example to FIG. 1 , wherethe electrical connections 111 (e.g. bond wires) need to be placedbefore mounting the second semiconductor die, which complicates theprocessing.

It is an advantage that this sensor device does not require a spacer orinterposer to be mounted between the first and second semiconductor die,although in some embodiments it may.

It is a major advantage that the first sensor and the second sensorstructure can measure a physical quantity, e.g. magnetic field atsubstantially the same 3D location. Such a sensor device is ideallysuited for automotive applications where redundancy is required.

The first semiconductor die may be mechanically mounted to the leadframe in any suitable way, for example by means of an insulating tapebetween the lead frame and the first semiconductor die.

The present invention also provides a sensor device comprising: a leadframe; two identical semiconductor dies comprising a first semiconductordie and a second semiconductor die, each die having a rectangular shapewith a geometrical center, and each die comprising a sensor structuresituated at a sensor location offset from its geometrical center; thesecond semiconductor die being stacked on top of the first semiconductordie, and being rotated over a non-zero angle, and optionally alsoshifted with respect to the first semiconductor die such that anorthogonal projection of the first and second sensor location L1, L2substantially coincide.

It is a major advantage of using two identical semiconductor dies (atleast hardware-wise), because this simplifies the design, testing andevaluation of the semiconductor dies.

In an embodiment, the sensor device comprises only two semiconductordies, namely said first semiconductor die and said second semiconductordie.

In an embodiment, the first semiconductor die comprises a plurality offirst bond pads, and the second semiconductor die comprises a pluralityof second bond pads, wherein the plurality of first and second bond padsof the stacked dies are exposed for allowing wire-bonding. In anembodiment, the first semiconductor die comprises a plurality of firstbond pads wire-bonded to the lead frame; and wherein the secondsemiconductor die comprises a plurality of second bond pads wire-bondedto the lead frame. In this embodiment, the electrical connection to thelead frame is implemented by means of bond-wires or wire-bonding. It isan advantage that, thanks to the rotation and offset or shift of the twosemiconductor dies, the bond pads are exposed at the top side, so thatthey can easily be wire-bonded.

In an embodiment, the relative position of the first sensor locationwith respect to the first rectangular shape is identical to the relativeposition of the second sensor location with respect to the secondsemiconductor die. In this embodiment, the layout may be identical, butthat is not absolutely required. It suffices that the layout is similar.

In an embodiment, the second semiconductor die has a layout identical tothat of the first semiconductor die. With having an “identical layout”is meant that a single set a of masks can be used. While not absolutelyrequired for the present invention to work, it is an advantage ofembodiments wherein the first and the second semiconductor die areidentical, because it largely simplifies the design, characterisation,qualification testing, logistics, assembly, etc.

In certain embodiments, the first semiconductor die is obtained from thesame silicon wafer as that of the second semiconductor die.

In other embodiments, the first semiconductor die is obtained from adifferent silicon wafer as that of the second semiconductor die.

In an embodiment, the stacked dies overlap at least by 60%, or at leastby 70%, or at least by 80%, or at least by 90% of the die area.

In an embodiment, the rectangular shape is a square. (having a ratio ofLength/Width=1).

In an embodiment, the rectangular shape is not square, having a ratio ofLength/Width>1.05).

In an embodiment the first semiconductor die is implemented in a firstsemiconductor technology (e.g. CMOS at a certain technology node, e.g.90 nm), and the second semiconductor die is implemented in a secondsemiconductor technology different from the first semiconductortechnology (e.g. CMOS at different technology node). For example, theresolution and/or the accuracy of the measurement provided by the firstsemiconductor die may be better than that of the second semiconductordie, but the second measurement may still be sufficiently accurate toact as a redundant measurement for safety purposes.

In an embodiment, the first rectangular shape has a length defining alength direction (X) and a width defining a width direction (Y)perpendicular to the length direction (X), said length being equal to orlarger than said width; and the first sensor location (L1) is offsetfrom a geometrical center of the first semiconductor die by a firstpredetermined offset (dx) along the length direction, and by a secondpredetermined offset (dy) in the width direction, wherein at least oneof the first and second offset is different from zero.

In an embodiment, one of the first and second predefined offset is equalto zero, and the other of the first and second predefined offset isdifferent from zero.

In an embodiment, each of the first and second predefined distance isdifferent from zero.

In an embodiment, the second semiconductor die is rotated over 180° withrespect to the first semiconductor die about an imaginary axisperpendicular to the lead frame; and the second semiconductor die isshifted in the first direction by a first distance equal to twice thefirst predefined offset, and is shifted in the second direction by asecond distance equal to twice the second predefined offset.

In an embodiment, the second semiconductor die is rotated over 90° withrespect to the first semiconductor die about an imaginary axisperpendicular to the lead frame.

In an embodiment, the first and second semiconductor die are square andare rotated over 90° relative to each other (e.g. as shown in FIG. 19 ).

In an embodiment, the first and second semiconductor die are non-square(i.e. are rectangular with a length larger than a width) and are rotatedover 90° relative to each other (e.g. as shown in FIG. 20 , FIG. 21 orFIG. 22 ).

In an embodiment, the second semiconductor die is rotated over an anglein the range from 10° to 85° with respect to the first semiconductor dieabout an imaginary axis perpendicular to the lead frame, for example asshown in FIG. 23 and FIG. 24 .

In an embodiment, the first and second semiconductor dies are located onthe same side of the lead frame, or stated in other words, the firstsemiconductor die is located between the lead frame and the secondsemiconductor die.

In an embodiment, each of said first and second semiconductor die has anactive side and a passive side, and wherein the active side of the firstsemiconductor die is oriented in the same direction as the active sideof the second semiconductor die.

In an embodiment the active sides of the first and the secondsemiconductor dies are both oriented away from, i.e. facing away fromthe lead frame.

In an embodiment the active sides of the first and the secondsemiconductor dies are both oriented towards, i.e. facing the leadframe.

In an embodiment, the second semiconductor die is flipped (i.e. turnedupside-down) with respect to the first semiconductor die, such that theactive side of the first semiconductor die and the active side of thesecond semiconductor die are facing each other.

In an embodiment, the second semiconductor die is flipped (i.e. turnedupside-down) with respect to the first semiconductor die, such that theactive side of the first semiconductor die and the active side of thesecond semiconductor die are facing away from each other.

In an embodiment, each of the first and second semiconductor die has athickness of at most 300 μm, or at most 250 μm, or at most 200 μm, or atmost 175 μm, or at most 150 μm, or at most 125 μm, or at most 100 μm, orat most 75 μm, or at most 50 μm. Such semiconductor dies are known as“thinned semiconductor dies”. Processes for producing “thinned wafers”(e.g. using etching techniques) are well known in the art and hence neednot be described in more detail here. Using thinned wafers and/or directstacking on top of each other (see further) offers the advantage thatthe first and second sensor can be even closer together (as compared tostandard wafers having a typical thickness of about 750 micron), hence adifference between the signals measured by the first and second sensor,or values derived therefrom, can be further reduced.

In an embodiment, the second semiconductor die is stacked directly ontop of the first semiconductor die, without a spacer or interposer. Itis an advantage of direct stacking that no additional component (e.g. aspacer or interposer) is required, thus saving material. It is a furtheradvantage that the sensors are located closer together.

In an embodiment, the second semiconductor die is stacked on top of thefirst semiconductor die with a layer of glue in between.

In an embodiment, the second semiconductor die is stacked on top of thefirst semiconductor die using an intermediate isolation layer. It is anadvantage of such intermediate isolation layer that the galvanicseparation between the two semiconductor dies can be further improved(as compared to a passivation layer at the bottom of the secondsemiconductor die).

In an embodiment, the first semiconductor die is galvanically separatedfrom the second semiconductor die.

In preferred embodiments, the two semiconductor dies are galvanicallyisolated from each other (at package level, maybe not atprinted-circuit-board (PCB) level.

Preferably the two semiconductor dies use different pins for groundingand for power supply.

In an embodiment, the first sensor structure on the first semiconductordie is identical to the second sensor structure on the secondsemiconductor die, for example as shown in FIG. 15 and FIG. 16 .

In an embodiment, the first sensor structure on the first semiconductordie is different from the second sensor structure on the secondsemiconductor die, for example as shown in FIG. 18 .

In both cases, the first and second silicon die are configured toperform the same overall function, for example to determine an angularposition based on magnetic measurements, but the actual implementation,for example the type of sensitive elements and/or the physicalarrangement of the sensitive elements may be different. As an example,the first sensor structure may contain horizontal Hall elements, whilethe second sensor structure contains vertical Hall elements. As anotherexample, both sensor structures contain a plurality of vertical Hallelements arranged on a circle with the same diameter, but the verticalHall elements of the first silicon die are arranged to measure acircumferential magnetic field component (tangential to the imaginarycircle), whereas the vertical Hall elements of the second silicon dieare configured to measure at a radial magnetic field component. Such asensor device is very useful for functional safety, for example to avoid“common cause” failure modes.

In an embodiment, only one of the first and second predefined distanceis zero, (thus the other predefined distance is different from zero).

In an embodiment, the first and second semiconductor die are square, andthe first predetermined offset is non-zero, and the second predeterminedoffset is zero; and the second semiconductor die is shifted with respectto each of the edges of the first semiconductor die by saidpredetermined offset (DX=dx and DY=dx), as illustrated for example inFIG. 19 .

In an embodiment, each of the first and second predefined distance isdifferent from zero.

In an embodiment, the first and second semiconductor dies have bond padslocated adjacent only one edge of the rectangle or square shape (seee.g. FIG. 15 , FIG. 16 , FIG. 18 to FIG. 20 , FIG. 22 to FIG. 24 ).

In an embodiment, the first and second semiconductor dies have bond padslocated adjacent two edges of the rectangle or square shape (see e.g.FIG. 21 ).

In an embodiment, the first sensor structure and the second sensorstructure are magnetic sensor structures.

In an embodiment, the sensor device is a redundant linear positionsensor device for use in automotive applications.

In an embodiment, the sensor device is a redundant angular positionsensor device for use in automotive applications.

In an embodiment, the first and second sensor structure comprises one ormore magnetic sensitive elements and optionally one or more integratedmagnetic concentrators (IMC). The magnetic sensitive elements can forexample be selected from the group consisting of a horizontal Hallelement, a vertical Hall element, a circular Hall element, amagneto-resistive element, e.g. an XMR element, GMR element, TMRelement, or combinations hereof. The magnetic sensor structures may beconfigured for measuring at least one magnetic quantity, for example onemagnetic field component (e.g. Bx, By, Bz), or two magnetic fieldcomponents (e.g. Bx and Bz) at substantially the same location, or amagnetic field gradient (e.g. dBx/dx, dBx/dy, dBy/dx, dBy/dx, dBz/dx,dBz/dy).

In an embodiment, the first sensor structure and the second sensorstructure each contain a single magnetic sensitive element (for exampleselected from the group consisting of: a horizontal Hall element, avertical Hall element, a circular Hall element, a magneto-resistiveelement, a GMR element, an XMR element, a TMR element).

In an embodiment, the first sensor structure and the second sensorstructure each contain a plurality of magnetic sensitive elements.

The “sensor structure” may comprise two sensors spaced apart over apredefined distance, each sensor comprising for example two horizontalHall elements and an IMC. Such “sensor structure” is capable ofmeasuring an in-plane field gradient (e.g. dBx/dx or dBz/dx).

In an embodiment, the first sensor structure and the second sensorstructure each contain one or more integrated magnetic concentrators,and the semiconductor dies have a thickness of at least 100 micron, orat least 125 micron, or at least 150 micron, or at least 175 micron, orat least 200 micron, but preferably less than 500 micron, or less than350 micron.

In an embodiment, the first sensor or the first sensor group on thefirst semiconductor die, and the second sensor or the second sensorgroup on the second semiconductor die comprises one or more horizontalHall elements with one or more integrated magnetic concentrators.

In an embodiment, the first sensor or the first sensor group on thefirst semiconductor die, and the second sensor or the second sensorgroup on the second semiconductor die comprises one or more horizontalHall elements without integrated magnetic concentrators.

In an embodiment, the first sensor or the first sensor group on thefirst semiconductor die, and the second sensor or the second sensorgroup on the second semiconductor die comprises one or more verticalHall elements; and/or TMR, GMR, AMR.

In an embodiment, the first sensor or the first sensor group on thefirst semiconductor die, and the second sensor or the second sensorgroup on the second semiconductor die comprises one or moremagneto-resistive elements.

In an embodiment, the first and second sensor structure are MEMs sensordevices, for example an accelerometer, a gyroscope, etc.

In an embodiment, each of the semiconductor dies comprises aprogrammable processor and a non-volatile memory, and these processorsare configured for running identical software instructions stored in thenon-volatile memory. In this case, external compensation (e.g. by anexternal ECU) may be needed to compensate for the 90° or 180° (or otherangle) rotation of the two semiconductor dies.

In an embodiment, each of the semiconductor dies comprises aprogrammable processor and a non-volatile memory, and both processorsare configured for determining an angular position, but one of theprocessors is configured for additionally compensating the rotation ofthe two semiconductor dies, such that both semiconductor dies providesubstantially the same value. In this case, external compensation (e.g.by an external ECU) is not required. This is a major advantage, becauseit provides “true redundancy”.

In an embodiment, each of the first and second semiconductor die isconfigured for providing a linear or an angular position based onmagnetic field gradients. Using gradient signals offers the advantagethat the measurement is substantially independent of an externaldisturbance field.

According to a second aspect, the present invention also provides asensor system comprising: a magnetic sensor device according to certainembodiments of the first aspect; and a magnetic source arranged in thevicinity of the magnetic sensor device.

In an embodiment, said magnetic source comprises at least one permanentmagnet.

The permanent magnet may be an axially or diametrically magnetizedcylindrical or ring-shaped or disk-shaped magnet, forming a dipole,quadrupole or higher-order magnetic field.

In an embodiment the sensor system may be connected to, or furthercomprise an external processor, for example an ECU (Engine Control Unit)in an automotive environment.

Use of sensor device or a sensor system as described above, forperforming a measurement and the redundant measurement in an automotiveenvironment, for improved reliability.

Particular and preferred aspects of the invention are set out in theaccompanying independent and dependent claims. Features from thedependent claims may be combined with features of the independent claimsand with features of other dependent claims as appropriate and notmerely as explicitly set out in the claims.

These and other aspects of the invention will be apparent from andelucidated with reference to the embodiment(s) described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 to FIG. 3 show three prior-art approaches for integrating twosensors on two dies to form a redundant sensor package.

FIG. 1 shows an assembly with two identical dies separated by a spaceror interposer.

FIG. 2 shows an assembly with two identical dies without a spacer orinterposer.

FIG. 3 shows an assembly with two identical dies located on oppositesides of a lead frame.

FIG. 4 , with FIGS. 4(a) and 4(b), FIG. 5 with FIGS. 5(a) and 5(b), andFIG. 6 with FIGS. 6(a) and 6(b), illustrate a disadvantageous effect ofnon-alignment of magnetic sensors as would be obtained by some prior artsystems comprising a magnet and a sensor device, in a so called“on-axis” assembly, an “off-axis” assembly, and a “through shaft”assembly, respectively.

FIG. 7 to FIG. 9 illustrate a first exemplary embodiment of the presentinvention.

FIG. 7 shows a first exemplary rectangular semiconductor die having asensor (or sensor structure) which is offset from the geometric centerof the die in the width direction (Y), in top view.

FIG. 8 shows a stack of two semiconductor dies shown in FIG. 7 in topview, after shifting and rotating the upper die by 180°, as can be usedin embodiments of the present invention.

FIG. 9 shows the stack of FIG. 8 in side view, wire-bonded to a leadframe, as can be used in sensor devices according to embodiments of thepresent invention.

FIG. 10 to FIG. 11 illustrate a second exemplary embodiment of thepresent invention.

FIG. 10 shows a second exemplary rectangular semiconductor die having asensor (or sensor structure) which is offset from the geometric centerof the die in both the length (X) and the width (Y) direction.

FIG. 11 shows a stack of two semiconductor dies shown in FIG. 10 , aftershifting and rotating the upper die by 180° such that the sensorelements are vertically aligned, as can be used in embodiments of thepresent invention.

FIG. 12 is a schematic representation of a so called “on-axis assembly”of a magnet and a sensor device according to an embodiment of thepresent invention.

FIG. 13 is a schematic representation of a so called “off-axis assembly”of a magnet and a sensor device according to an embodiment of thepresent invention.

FIG. 14 is a schematic representation of a so called “through shaft”assembly of a magnet and a sensor device according to an embodiment ofthe present invention.

FIG. 15 is a schematic representation showing another exemplaryembodiment of the present invention, which can be seen as a specificexample of FIG. 9 , where a magnetic sensor structure is used comprisingeight horizontal Hall elements located on a circle.

FIG. 16 is a schematic representation showing another exemplaryembodiment of the present invention, which can be seen as anotherspecific example of FIG. 9 , where a magnetic sensor structure is usedcomprising six vertical Hall elements located on a circle, and orientedfor measuring a radial field component.

FIG. 17(a) to FIG. 17(f) show several other exemplary magnetic sensorstructures which can also be used in the first and second semiconductordie of exemplary sensor devices according to embodiments of the presentinvention, shown in top view rather than perspective view, forillustrative purposes. But the present invention is not limited thereto,and other sensor structures can also be used.

FIG. 18 shows another “stacked die assembly” according to an embodimentof the present invention, where the first and second semiconductor diehave identical outer dimensions, but different magnetic sensorstructures. The magnetic sensor structures are located offset from thegeometric centers of the respective dies, and the dies are shifted androtated relative to each other, such that the sensor structures arevertically aligned.

FIG. 19(a) shows a square semiconductor die having a sensor structurewhich is offset from the geometric center of the die in a directionparallel to one of its edges, in top view.

FIG. 19(b) shows a stack of two semiconductor dies as shown in FIG.19(a) in top view, after rotating the upper die by 90° and aftershifting the upper die so as to align the magnetic centers of the sensorstructures, according to an embodiment of the present invention.

FIG. 20(a) shows a rectangular semiconductor die having a sensor whichis offset from the geometric center of the die in a direction parallelto one of its edges, in top view. The die has bond pads on only oneside.

FIG. 20(b) shows a stack of two semiconductor dies shown in FIG. 20(a)in top view, after rotating the upper die by 90° and after shifting theupper die so as to vertically align the sensors, according to anembodiment of the present invention.

FIG. 21(a) shows a rectangular semiconductor die having a sensor whichis offset from the geometric center of the die in a direction parallelto one of its edges, in top view. The die has bond pads on two sides.

FIG. 21(b) shows a stack of two semiconductor dies shown in FIG. 21(a)in top view, after rotating the upper die by 90° and after shifting theupper die so as to vertically align the sensors, according to anembodiment of the present invention.

FIG. 22(a) shows a rectangular semiconductor die having a sensor whichis offset from the geometric center of the die in two directionsparallel to each of its edges, in top view.

FIG. 22(b) shows a stack of two semiconductor dies shown in FIG. 22(a)in top view, after rotating the upper die by 90° and after shifting theupper die so as to vertically align the sensors, according to anembodiment of the present invention.

FIG. 23 shows a stack of two square semiconductor dies in top view, eachdie having a sensor which is offset from the geometric center of the dieand is located at a position near the corner. The dies are stacked afterrotating the upper die over about 15°, and after shifting the upper dieso as to vertically align the sensors, according to an embodiment of thepresent invention.

FIG. 24 shows a stack of two square semiconductor dies in top view, eachdie having a sensor which is offset from its geometrical center byapproximately 25% of the width of the die. The dies are stacked afterrotating the upper die over about 15°, and after shifting the upper dieso as to vertically align the sensors, according to an embodiment of thepresent invention.

The drawings are only schematic and are non-limiting. In the drawings,the size of some of the elements may be exaggerated and not drawn onscale for illustrative purposes. Any reference signs in the claims shallnot be construed as limiting the scope. In the different drawings, thesame reference signs refer to the same or analogous elements.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The present invention will be described with respect to particularembodiments and with reference to certain drawings, but the invention isnot limited thereto but only by the claims. The drawings described areonly schematic and are non-limiting. In the drawings, the size of someof the elements may be exaggerated and not drawn on scale forillustrative purposes. The dimensions and the relative dimensions do notcorrespond to actual reductions to practice of the invention.

Furthermore, the terms first, second and the like in the description andin the claims, are used for distinguishing between similar elements andnot necessarily for describing a sequence, either temporally, spatially,in ranking or in any other manner. It is to be understood that the termsso used are interchangeable under appropriate circumstances and that theembodiments of the invention described herein are capable of operationin other sequences than described or illustrated herein.

Moreover, the terms top, under and the like in the description and theclaims are used for descriptive purposes and not necessarily fordescribing relative positions. It is to be understood that the terms soused are interchangeable under appropriate circumstances and that theembodiments of the invention described herein are capable of operationin other orientations than described or illustrated herein.

It is to be noticed that the term “comprising”, used in the claims,should not be interpreted as being restricted to the means listedthereafter; it does not exclude other elements or steps. It is thus tobe interpreted as specifying the presence of the stated features,integers, steps or components as referred to, but does not preclude thepresence or addition of one or more other features, integers, steps orcomponents, or groups thereof. Thus, the scope of the expression “adevice comprising means A and B” should not be limited to devicesconsisting only of components A and B. It means that with respect to thepresent invention, the only relevant components of the device are A andB.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the present invention. Thus, appearancesof the phrases “in one embodiment” or “in an embodiment” in variousplaces throughout this specification are not necessarily all referringto the same embodiment but may. Furthermore, the particular features,structures or characteristics may be combined in any suitable manner, aswould be apparent to one of ordinary skill in the art from thisdisclosure, in one or more embodiments.

Similarly, it should be appreciated that in the description of exemplaryembodiments of the invention, various features of the invention aresometimes grouped together in a single embodiment, figure, ordescription thereof for the purpose of streamlining the disclosure andaiding in the understanding of one or more of the various inventiveaspects. This method of disclosure, however, is not to be interpreted asreflecting an intention that the claimed invention requires morefeatures than are expressly recited in each claim. Rather, as thefollowing claims reflect, inventive aspects lie in less than allfeatures of a single foregoing disclosed embodiment. Thus, the claimsfollowing the detailed description are hereby expressly incorporatedinto this detailed description, with each claim standing on its own as aseparate embodiment of this invention.

Furthermore, while some embodiments described herein include some butnot other features included in other embodiments, combinations offeatures of different embodiments are meant to be within the scope ofthe invention, and form different embodiments, as would be understood bythose in the art. For example, in the following claims, any of theclaimed embodiments can be used in any combination.

In the description provided herein, numerous specific details are setforth. However, it is understood that embodiments of the invention maybe practiced without these specific details. In other instances,well-known methods, structures and techniques have not been shown indetail in order not to obscure an understanding of this description.

In this document, the term “sensor” or “sensor structure” is to beinterpreted broadly, as referring to a single sensor component or sensorelement or a plurality of components or a structure for measuring aphysical quantity, for example a MEMs structure, an accelerometer, agyroscope, a “magnetic sensor structure” comprising a single or aplurality of magnetic sensitive elements with or without integratedmagnetic concentrators.

In this document, the term “magnetic sensor element” or “magneticsensor” can refer to a component or a group of components or asub-circuit or a structure capable of measuring a magnetic quantity,such as for example a magneto-resistive element, a GMR element, an XMRelement, a TMR element, a horizontal Hall plate, a vertical Hall plate,a circular Hall element, a Wheatstone-bridge containing at least one(but preferably four) magneto-resistive elements, etc. or combinationshereof.

In certain embodiments of the present invention, the “magnetic sensorstructure” may comprise one or more integrated magnetic concentrators(IMC) and one or more horizontal Hall elements, for example a diskshaped IMC and two or four horizontal Hall elements arranged near theperiphery of the IMC, for example as illustrated in FIG. 17(b) or asillustrated in FIG. 17(e).

The phrase “the geometrical center is offset from the sensor location”means the same as “the sensor location is offset from the geometricalcenter”, meaning that they do not coincide.

The present invention relates to the field of sensor devices, and morein particular to a sensor device for use in an automotive environment.The device comprising two semiconductor dies for performing a dualmeasurement, e.g. one for performing an actual measurement and one forperforming a redundant measurement, as can be used for safety purposes.

While the invention works for several kinds of sensors, e.g.micro-electro-mechanical systems (MEMs) such as accelerometers orgyroscopes, magnetic sensors, and other sensors, the present inventionwill be described primarily for magnetic sensors, to simplify thedescription, but the present invention is not limited thereto.

As stated in the background section, dual or redundant sensor devicesare known in the art. Such devices typically comprise two substrates ina single package, one for providing a first sensor measurement (e.g. anactual sensor measurement), the other for providing a second measurement(e.g. a redundant sensor measurement). Devices in which two substratesare placed side by side require a relatively large footprint, thusrequire more board space, which is undesirable. In order to decrease thefootprint, the substrates can be stacked on top of each other, forexample as shown in FIG. 1 to FIG. 3 , showing three existing solutionsfor integrating two sensors, one on each die, to form a redundant sensorpackage.

FIG. 1 shows an assembly 100 with two identical substrates 102 a, 102 b,stacked on top of each other with an intermediate spacer or interposer103. The first substrate 102 a has a first sensor 104 a. The secondsubstrate 102 b has a second sensor 104 b. The two substrates arealigned, and also the two sensors are aligned (in the Z-direction). Thefirst substrate 102 a is connected to the lead frame 109 via firstbonding wires 112 a. The second substrate 102 b is connected to the leadframe 109 via second bonding wires 112 b. A disadvantage of thisassembly 100 is that it requires a spacer 103 (also referred to asinterposer) to allow the first substrate 102 a to be wire bonded to thelead frame 109. The spacer 103 increases the bill of material, increasesthe height of the package, increases the distance between the twosensors 104 a, 104 b (in the height direction), and complicates theassembly process.

FIG. 2 shows an assembly with two identical substrates 202 a, 202 bwithout a spacer or interposer. The first substrate 202 a has a firstsensor 204 a. The second substrate 202 b has a second sensor 204 b. Thesecond substrate 202 b is shifted with respect to the first substrate202 a (in the X-direction) for exposing bond pads of the first substrate202 a, so that these can be wire bonded to the lead frame 209. The twosensors 204 a, 204 b are misaligned.

FIG. 3 shows an assembly with two identical substrates 302 a, 302 bmounted to opposite sides of a lead frame 309. The first substrate 302 ahas a first sensor 304 a. The second substrate 302 b has a second sensor304 b. As can be seen, the first substrate 302 a is aligned to thesecond substrate 302 b, and the first sensor 304 a is aligned to thesecond sensor 304 b. The two sensors are separated by the thickness ofthe lead frame 309. However, bonding on both the upper side and thelower side of the lead frame 309 is not a standard process, andconsiderably complicates the assembly process.

While sensor misalignment may not be a problem in certain applications,for example sensors to measure the earth's gravitational field, sensormisalignment is of concern in certain applications such as for examplemagnetic sensor systems, e.g. linear or angular position sensor systems.

FIG. 4 to FIG. 6 illustrate a problem when using a sensor device 401,501, 601 with a sensor configuration as shown in FIG. 2 , in an angularposition sensor system comprising a permanent magnet 411, 511, 611respectively. FIG. 4 shows a so called “on-axis” arrangement. FIG. 5shows a so called “off-axis” arrangement. FIG. 6 shows a so called“through shaft” arrangement respectively.

It is noted that the sensors are schematically represented by a blacksquare in order not to complicate the drawings, but of course inpractice the sensors may have a (much) more complicated structure (seefor example FIG. 15 to FIG. 18 ).

It can be easily understood that the first sensor 404 a, 504 a, 604 awill provide another value than the second sensor 404 b, 504 b, 604 b,because it is located at a different location (typically at least 1 mmapart, or at least 750 micron apart, or at least 500 micron apart). Thelarger the distance between the sensor locations, the larger thedeviation between the sensor signals, which is undesirable. In an idealdual sensor device, the first substrate would provide exactly the samesignal as the second substrate. This offers the advantage that thethreshold for detecting an error or a fault condition can be decreased.

The inventors of the present invention were asked to provide a sensordevice with a better match between the measurement results (e.g. angularposition) provided by the two semiconductor dies, but preferably withoutthe disadvantages of the prior art, in particular without significantlyincreasing the package thickness, and/or without significantlyincreasing material cost, and/or without significantly complicating theassembly process, and preferably all of these.

Facing this challenge, and after many considerations, the inventorssurprisingly came to the idea of providing a sensor device comprising alead frame, a first semiconductor die electrically connected to the leadframe, and a second semiconductor die electrically connected to the leadframe. The first semiconductor die comprising a first sensor or sensorstructure situated at a first sensor location, the second semiconductordie comprising a second sensor or sensor structure situated at a secondsensor location. The first semiconductor die has a first rectangularshape with a first geometrical center offset from the first sensorlocation. The second semiconductor die has a second rectangular shapeequal to the first rectangular shape and has a second geometric centeroffset from the second sensor location. The second semiconductor die isstacked on top of the first semiconductor die, and rotated over anon-zero angle, and optionally also shifted over a non-zero distancewith respect to the first semiconductor die such that an orthogonalprojection of the first and second sensor locations onto the lead framecoincide.

Stated in simple terms, such a sensor device can be referred to as a“stacked die assembly” comprising two semiconductor dies, wherein thetwo sensor structures are “aligned” and can easily be bonded in thestandard manner (from the top). In case the electrical connection isdone using wire-bonding, such an assembly is also referred to as a“wire-bonded stacked die assembly”. Preferably, the stacked die assemblyis over moulded with a plastic compound, to form a “(wire bonded)stacked chip package” (not shown).

The first sensor or sensor structure comprises one or more sensorelements, e.g. magnetic sensitive elements, and optionally furtherelements (e.g. integrated magnetic concentrator). Likewise, the secondsensor or sensor structure comprises one or more sensor elements, e.g.magnetic sensitive elements, and optionally further elements (e.g.integrated magnetic concentrator).

With “sensor location” (for example L1 in FIG. 15 ) is meant a (real orimaginary) central location defined by the one or more sensitiveelements, for example substantially in the middle between the sensitiveelements. For example, in case of a single sensitive element, the“sensor location” is defined as the location of the single sensitiveelement. In case of a sensor structure having a plurality of sensitiveelements arranged on a virtual circle, the “sensor location” is definedas the centre of the virtual circle. In case of a sensor structurehaving two spaced apart sensing elements, the “sensor location” isdefined as the location in the middle between the two sensing elements,etc.

The inventors surprisingly found a unique and very advantageouscombination of technical features, namely: (1) two semiconductor dies,(2) stacked on top of each other, (3) both dies having a sensor locationwhich is offset from a geometrical center of the die (not located in themiddle), (4+5) the upper die is rotated (4) and shifted (5) with respectto the lower die such that a perpendicular projection of the sensorcoincide.

This unique combination offers the advantage that the two sensorlocations are “vertically aligned”, so that the first and second sensorcan measure substantially the same physical (e.g. magnetic) quantity orquantities, contrary to the stack shown in FIG. 2 , where the first andsecond sensor locations are offset in at least one direction parallel tothe lead frame.

Preferably each of the dies further comprises bond pads located on theiractive surface, which bond pads are preferably exposed at their top-sidewhen the dies are stacked. This facilitates easy wire-bonding from thetop.

It is a major advantage of this magnetic sensor device that theelectrical connections, e.g. wire-bonding can be performed on the topside, in a simple manner, using standard equipment, contrary to FIG. 1 ,where the bond wires 111 need to be placed before mounting the secondsemiconductor die, which complicates the processing.

It is an advantage that the stacked arrangement proposed by the presentinvention does not require a spacer or interposer to be mounted betweenthe first and second semiconductor die, although in some embodiments itmay.

It is a major advantage that the first sensor and the second sensor canmeasure the physical quantity, e.g. magnetic field at substantially thesame 2D or even 3D location. Such a sensor device is ideally suited forautomotive applications where redundancy is required for safety reasons.

It is noted in this respect that “redundancy” does not require thatexactly the same circuitry is used on the first and second semiconductordie, and/or that exactly the same physical quantity/quantities is/are tobe measured at exactly the same physical location(s) (see e.g. FIG. 16where individual sensor elements are not aligned, but the sensors as awhole are aligned), and/or that the measurement results or valuesderived therefrom need to be exactly the same (e.g. an angle measured bythe first semiconductor die of FIG. 9 may be 180° phase shifted withrespect to an angle measured by the second semiconductor die), but themeasurement results or values derived therefrom obtained from the firstsemiconductor die are consistent with those obtained from the secondsemiconductor die.

While not absolutely necessary (see e.g. FIG. 18 ), in preferredembodiments, the first semiconductor die is exactly the same as thesecond semiconductor die (meaning: is made using all of the same masks).If both obtained from the same wafer, this may further improve the matchof the results provided by the first and second semiconductor die. Iftaken from different wafers, this may reduce the risk of a common causefailure mode related to wafer processing.

In preferred embodiments the semiconductor dies are stacked directly ontop of each other (without an intermediate component or layer), and arepreferably thinned to a thickness less than 350 μm, e.g. less than 300μm, e.g. less than 250 μm, e.g. equal to about 200 μm, or even less than200 μm. This has the effect of further decreasing the distance betweenthe sensor structure of the first and second semiconductor die andfurther improves the match of the results. This effect is not offered byany of the prior art solutions known to the inventors. In fact, in orderto obtain this effect, only the upper die needs to be thinned. In someembodiments the lower die has its normal thickness, which may improvemechanical stiffness or mechanical robustness.

In preferred embodiments the two semiconductor dies are galvanicallyseparated from each other including the power and ground lines, meaning(inter alia) that the two semiconductor dies are wire-bonded todifferent pins of the package, for true redundancy.

These are the main underlying ideas of the present invention, which willbe described in more detail further.

FIG. 1 to FIG. 6 are already described above.

FIG. 7 to FIG. 9 illustrate a first exemplary sensor device 900, and thesemiconductor dies used therein.

FIG. 7 shows a rectangular semiconductor die 702 having a length L (inthe X-direction) and a width W (in the Y-direction), in top view. Thelength L is equal to, or larger than the width W. The rectangle has ageometric center 706, schematically indicated by a star, which islocated at the intersection of two diagonals (not shown in FIG. 7 , butsee e.g. FIG. 20 a ), which is the same as the intersection of two linesparallel to the length direction and width direction halfway the lengthand the width (as shown in FIG. 7 ).

The semiconductor die 702 comprises a sensor or sensor structure 704,schematically represented by a square, in order not to complicate thedrawing, having a “sensor location” L1 (e.g. in case of a magneticsensor structure, known as the “magnetic centre”) which, in thisexample, is offset from the geometric center 706 in the Y-direction by apredefined distance “dy”. Examples of “sensor location” will be providedfurther (see e.g. “L1” and “L2” in FIG. 15 to FIG. 18 ), but stated insimple terms, the sensor location is a point located substantially “inthe middle” of, or in the middle between the one or more sensitiveelements.

The semiconductor die 702 preferably further comprises a zone 708comprising a plurality of bond pads 707. This zone is located on an edgeof the rectangle, (in the example on only one edge), and has a width ofat most twice said offset “dy”, thus, the width of zone 708≤2*dy. Orstated differently, for a given width of the pad zone 708, the offset“dy” between the sensor location and the geometrical center has to be atleast 50% of said width. In preferred embodiments, this width has avalue in the range from 110 to 250 μm, or from about 150 to about 210μm, for allowing electrical connection to the lead frame, e.g. viawire-bonding, but the invention would also work with larger zones, forexample a zone having a width up to 250 μm, or up to 300 μm, or up to400 μm, or up to 450 μm.

FIG. 8 shows a stack 800 of two semiconductor dies 802 a, 802 b havingthe geometry (i.e. size and shape and relative location of the sensorstructure and the bond pads) of FIG. 7 , after rotating the upper die802 b by 180° around an axis perpendicular to the semiconductor dies,and after optionally shifting the upper die 802 b such that the longedges of the upper and lower die are parallel but spaced apart by adistance DY equal to twice said offset dy, thus DY=2*dy. (forcompleteness, it is noted that, if the upper die is rotated about arotation axis passing through the sensor location L1, no translation isneeded).

As can be seen, by doing so, a stack is created in which a 2D projectionof the geometric centers 806 a, 806 b are spaced apart by 2*dy, but the2D projections of the sensor locations L1, L2 coincide. Thus, the sensorstructures 804 a and 804 b are “aligned”, meaning that they will measuresubstantially the same physical quantity. It is noted that, as willbecome clear further (see e.g. FIG. 16 ), the individual quantitiesmeasured by the sensitive elements of the first and second sensorstructure 804 a, 804 b may be different, but the measurement resultderived therefrom, for example an angular position, is substantiallyidentical for both semiconductor dies.

It is furthermore noted that the sensor locations L1, L2 do not exactlycoincide, but in reality, are spaced apart in the height direction bythe thickness of the upper die 802 b. However, for practical purposes,these two locations can be considered substantially “the same”,especially if the upper semiconductor die 802 b is “thinned”, forexample to a thickness lower than 350 micron, or lower than 250 micron,e.g. to about 200 micron. Moreover, in preferred embodiments of thepresent invention, the result measured by the sensor device as part ofan angular position sensor system is highly insensitive to axialdistance between the sensor device and the magnet anyway.

FIG. 9 shows the stack of FIG. 8 in side view, mounted on a lead frame9. As can be appreciated, bond pads 907 a of the first (lower)semiconductor die 902 a can be electrically connected, e.g. wire-bondedto the lead frame 909 by means of first bond-wires 912 a, and bond pads907 b of the second (upper) semiconductor die 902 b can be electricallyconnected, e.g. wire bonded to the lead frame 909 by means of secondbond wires 912 b, without problems.

In contrast to FIG. 1 , the semiconductor dies 902 a, 902 b of FIG. 9are rotated by 180° and their edges are offset from each other, and nointerposer is required. In contrast to FIG. 2 , the sensor structures ofFIG. 9 are aligned. In contrast to FIG. 3 , the two semiconductor diesof FIG. 9 are both located on the same side of the lead frame and theiractive surfaces are oriented in the same direction (upwards), andbonding is only required on one side of the lead frame. In other words,the solution offered by the present invention has all the benefits ofthe prior art solutions.

While not explicitly shown, the stack 900 of FIG. 9 can be overmouldedin known ways, e.g. by a plastic compound, to form a packagedsemiconductor device which can be used in automotive applications, forperforming an actual measurement and a redundant measurement, e.g. forimproving safety.

Preferably (as shown in FIG. 9 ) the two semiconductor dies 902 a, 902 bare directly stacked on top of each other, without an intermediatecomponent (e.g. spacer or interposer). And preferably, at least theupper die 902 b is thinned (not shown). This further decreases thedistance between the two sensor structures 904 a, 904 b.

While not explicitly shown in FIG. 9 , the first and secondsemiconductor die are preferably galvanically separated, includingseparate connection to ground and power supply pins. In order to providesufficient isolation, the backside of the semiconductor dies may beprovided with a passivation layer, for example an oxide layer or anitride layer or combinations hereof. Alternatively, or in addition,electrical separation can also be provided by means of an electricallyinsulating layer between the semiconductor dies, e.g. an insulatingtape, e.g. made of polyimide, e.g. having a thickness of about 50 to 100μm.

In another variant (not shown), the sensor 704 is offset from thegeometric centre in the X direction (length direction of the rectangle)rather than the Y direction (width direction of the rectangle), and thezone 708 with the bond pads 707 would be located near the short edge.

In another variant, the rectangle is a square, and the two dies arerotated over 180°.

FIG. 10 and FIG. 11 illustrate a second example of a silicon die 1002suitable for stacking, and a stacked die arrangement 1100 using two suchsilicon dies 1102 a, 1102 b, which can be seen as a variant of thestacked die arrangement 900 of FIG. 7 to FIG. 9 .

FIG. 10 shows a second exemplary semiconductor die 1002 in top view. Thesemiconductor die has a rectangular shape, the geometric centre 1006 ofwhich is indicated by a star. The semiconductor die has a sensorstructure 1004 (schematically represented by a square for illustrativepurposes) which is offset from the geometric centre 1006 by a predefineddistance “dx” in the length direction (X) and which is offset from thegeometric centre 1006 by a predefined distance “dy” in the widthdirection (Y). The semiconductor die has a plurality of bond pads 1007which are located in a rectangular zone 1008 along an edge of thesemiconductor die 1002 extending in the X-direction and having a widthof at most 2*dy, and/or in a zone 1018 along an edge of thesemiconductor die extending in the Y-direction and having a width of atmost 2*dx, together forming an L shape. Or for given dimensions of thezones 1008 and 1018, if present, the minimum offset dx and dy can bedetermined.

FIG. 11 shows a stack 1100 of two semiconductor dies 1102 a, 1102 bshown in FIG. 10 , after rotating the upper die by 180°, and afteroptionally shifting the upper die 1102 b such that the dies are offsetin the X direction by a distance DX=2dx, and in the Y-direction by adistance DY=2dy. (As mentioned above, if the rotation is performed aboutan axis passing through L1, L2, no translation is required, only therotation). As can be seen, this causes alignment of the sensor locationsL1, L2, so that the sensor structures 1104 a, 1104 b will measuresubstantially the same physical quantity, albeit rotated over 180°.

Similar as described in FIG. 7 to FIG. 9 , the two semiconductor dies1102 a, 1102 b may be thinned (e.g. to a thickness of about 100 to 350micron, e.g. equal to about 200 micron), may be stacked directly on topof each other or by means of an intermediate insulating layer orinsulating tape, are preferably galvanically separated including theprovision of separate ground and power supply lines, and the stackedassembly may be overmoulded.

FIG. 7 to FIG. 11 described two exemplary embodiments of a packagedstacked die arrangement comprising two sensor structures, which arealigned such that a projection of the sensors in a directionperpendicular to the lead frame coincide.

In practice, the semiconductor dies may further comprise biasingcircuitry for biasing the sensor structures, readout circuitry,amplification circuitry, digitisation circuitry, processing circuitry,etc., but since such circuits are not the main focus of the presentinvention, and are well known in the art, they need not be described infurther detail herein. Suffice it to say that the principles of thepresent invention can be used in combination with any magnetic sensorstructure, even sensor structures comprising integrated magneticconcentrators (IMC), provided that the alignment is sufficientlyaccurate, and that the thickness of the semiconductor dies is at least100 micron, or at least 150 micron, or at least 200 micron.

The fact that the second semiconductor die is rotated by 180° withrespect to the first semiconductor die, and may provide a measurementvalue (e.g. a rotation angle) different from that provided by the firstsemiconductor die, can easily be addressed by a post-processing step,which may be performed by the circuitry of one of the sensor devicesitself, which may e.g. be programmed for rotating the result by 180°, orby an external processor (e.g. an ECU). Mathematically, thepost-processing step can for example be as simple as adding 180° to theangle provided by the second semiconductor die, or subtracting 180°,such that the value lies in the range from 0° to 360°.

FIG. 12 to FIG. 14 show how sensor devices 1201, 1301, 1401 can improvethe matching between the results provided by the two semiconductor diescomprised therein.

FIG. 12 shows an exemplary sensor system 1200, more in particular anangular position sensor system, comprising a permanent disk magnet 1211and a sensor device 1201 in a so called “on-axis arrangement”. Thesensor device 1201 may for example have a stacked die arrangement asshown in FIG. 8 or FIG. 9 or FIG. 11 . The two sensor structures 1204 a,1204 b are schematically indicated by two black squares for illustrativereasons, which substantially coincide in 3D space, because the distancebetween them (in a direction perpendicular to the semiconductor dies) istypically only about 100 to 350 micron, e.g. about 200 micron, whereasthe distance “g” between the magnet 1211 and the sensor device 1201 istypically an order of magnitude larger (e.g. about 2.0 to 5.0 mm).

It will be appreciated that both sensor structures 1204 a, 1204 b of thesensor device 1201 are aligned with the rotation axis of the magnet1211, in contrast to FIG. 4 , where both sensor structures are offsetfrom said rotation axis. Furthermore, it can be appreciated that bothsensor structures 1204 a, 1204 b of the device 1201 will sensesubstantially the same magnetic field. Hence, not only the individualresults may be improved (related to unwanted offset from the rotationaxis), but especially the result provided by the first semiconductor dieand the second semiconductor die will be better matched (after takinginto account the 180° rotation, of course). This makes the sensor device1201 ideally suited for safety applications.

The example of FIG. 12 uses a disk-shaped magnet, but the presentinvention is not limited thereto and other magnets, such as bar magnetsor ring magnets may also be used. In addition, while the magnet 1211 ofFIG. 12 is a (e.g. diametrically magnetized or axially magnetized)two-pole magnet, higher order magnets may also be used, for example aquadrupole or a six-pole magnet. Of course, the sensor structure and/oralgorithm used inside the sensor device 1201 has to correspond to thespecific magnet being used, and with the location of the sensor devicewith respect to the magnet, in the example of FIG. 12 an on-axisposition, as is the case with existing solutions. The interested readercan find suitable sensors for example in WO2014029885A1, incorporatedherein by reference in its entirety, the present invention not beinglimited thereto.

FIG. 13 shows another exemplary sensor system 1300, more in particularan angular position sensor system, comprising a permanent disk magnet1311 and a sensor device 1301 in a so called “off-axis arrangement”. Thesame or similar remarks as given for FIG. 12 are also applicable here,mutatis mutandis.

Comparison of FIG. 13 and FIG. 5 shows that the sensor device 1301 doesnot suffer from the same angular offset problem of FIG. 5 , because thetwo sensor structures (indicated by a black square) substantiallycoincide, as described above.

Many variants of this system are contemplated, for example having a fourpole magnet and/or a ring magnet and/or a bar magnet and/or a specificsensor topology for measuring one or more magnetic field componentsand/or circuitry for determining one or more magnetic field gradients,and/or using a specific circuit or formula or algorithm for determininga linear or angular position based on one or more of these values. Asstated above, the main focus of the present invention is not to describesuch algorithms or such sensor topologies, the details of which aretherefore omitted from the present disclosure. The interested reader canfind suitable sensors for example in patent application EP19193068.4filed by the same applicant on 22 Aug. 2019, refiled on 14 Aug. 2020 aspatent application EP20191167.4, both of which are incorporated hereinby reference in their entirety, in particular FIG. 5 , FIG. 12 and FIG.13 thereof, and the associated text, the present invention not beinglimited thereto.

FIG. 14 shows another exemplary sensor system 1400, more in particularan angular position sensor system, comprising a permanent disk magnet1411 and a sensor device 1401 in a so called “through-shaft”arrangement. The same or similar remarks as given for FIG. 12 and FIG.13 are also applicable here, mutatis mutandis. Suitable sensorstructures are described for example in patent application EP19193068.4and/or EP20191167.4, in particular FIG. 15 thereof, and the associatedtext, the present invention not being limited thereto.

Comparison of FIG. 14 and FIG. 6 shows that the sensor device 1401 doesnot suffer from the same angular offset problem of FIG. 6 , because thetwo sensor structures of the two semiconductor dies of the presentinvention substantially coincide, as described above. Many variants ofthe system 1400 are contemplated, similar as described for FIG. 13 .

FIG. 15 is a schematic representation of an exemplary sensor device1500, having a lead frame 1509, electrically connected (e.g.wire-bonded) to two identical semiconductor dies 1502 a, 1502 b whichare stacked, rotated and offset or shifted in the manner shown in FIG. 9.

The main purpose of FIG. 15 is to show an particular example of a sensordevice according to the present invention, with a somewhat more complexsensor structure 1504, in this case consisting of eight horizontal Hallelements located on a circle, angularly spaced apart by 45° (describedin detail in WO2014029885A1). When used in an on-axis position (as inFIG. 12 of the present application) in conjunction with a magneticquadrupole, the circuitry on the first semiconductor die 1502 a iscapable of determining an angular position α1, and the circuitry on thesecond semiconductor die 1502 b is capable of determining an angularposition α2, which should be substantially equal to al within sometolerance margin, because the measurement range of these sensorstructures is limited from 0° to 180°.

It is interesting to note that in the example of FIG. 15 , individualsensor elements (here: horizontal Hall elements) of the first sensorstructure 1504 a of the lower semiconductor die 1502 a are located atsubstantially the same locations as individual sensor elements (here:horizontal Hall elements) of the second sensor structure 1504 b of theupper semiconductor die 1502 b, but that is not absolutely required, aswill be described further (see e.g. FIG. 16 ). What is important,however, is that the magnetic center L1 of the first sensor structure1504 a (here: the center of the circle on which the horizontal Hallelements are located) is aligned with the magnetic center L2 of thesecond sensor structure 1504 b. This example also illustrates that themagnetic center L1 does not need to be located on a magnetic sensitiveelement but may be located between them.

In a variant of this system (not shown), the sensor structure of thesecond semiconductor die 1502 b contains eight horizontal Hall elementslocated on a circle, spaced apart by 45°, but the radius of this circlebeing different (e.g. at least 10% larger or smaller) than the radius ofthe circle of the sensor structure of the first semiconductor die 1502a. In this case, the first and second semiconductor die have identicalouter dimensions, and the relative position of the magnetic sensorstructures is the same, but preferably also at least 50% of the othercircuitry of the two semiconductor devices is identical, whichsimplifies the design, testing and evaluation of the semiconductor die.

FIG. 16 is a schematic representation of another exemplary sensor device1600, having a lead frame 1609, electrically connected, e.g. wire-bondedto two identical semiconductor dies 1602 a, 1602 b which are stacked,rotated and offset or shifted in the manner shown in FIG. 9 .

The main purpose of FIG. 16 is to show another particular example of asensor device according to the present invention, with another somewhatcomplex sensor structure 1604, in this case consisting of six verticalHall elements located on a circle, angularly spaced apart in a specificmanner and oriented to measure a radial magnetic field component (asdescribed in more detail in WO2014029885A1). When used in an on-axisposition (as in FIG. 12 of the present application) in conjunction witha six-pole magnet, the circuitry (not shown) on the first semiconductordie 1602 a is capable of determining an angular position α1 (in therange from 0° to 120°), and the circuitry on the second semiconductordie 1602 b is capable of determining an angular position α2 (in therange from 0° to 120°), which should be substantially equal to(α1+60°+k*120°) within some tolerance margin, k being an integer value.

It is interesting to note that in the example of FIG. 16 , individualsensor elements (here: vertical Hall elements) of the first sensorstructure 1604 a of the lower semiconductor die 1602 a are not locatedat substantially the same locations as individual sensor elements of thesecond sensor structure 1604 b of the upper semiconductor die 1602 b,but between them. But that is OK, as long as the magnetic center L1 ofthe first sensor structure 1604 a (here: the center of the circle onwhich the vertical Hall elements are located) is aligned with themagnetic center L2 of the second sensor structure 1604 b.

As mentioned above, the present invention works with various sensorstructures, some examples of which are shown in FIG. 17(a) to FIG.17(f), together with a dot indicating the location of the “magneticcenter” thereof. In contrast to FIG. 15 and FIG. 16 , these sensorstructures are shown in top view, but displayed next to each otherrather than in perspective view, for illustrative purposes.

In FIG. 17(a), each sensor structure 4 a, 4 b has four vertical Hallelements. Such a sensor structure can for example be used to determinean angular position when used in conjunction with a dipole ring or diskmagnet, and when mounted in an off-axis position or in a through-shaftposition. (e.g. as described in more detail in patent applicationEP19193068.4 and/or EP20191167.4).

In FIG. 17(b), each sensor structure 4 a, 4 b has two sets of fourHorizontal Hall elements arranged at the periphery of a disk-shaped IMC.Such a sensor structure can for example be used to determine an angularposition when used in conjunction with a dipole ring or disk magnet, andwhen mounted in an off-axis position or in a through-shaft position(e.g. as described in more detail in patent application EP19193068.4and/or EP20191167.4).

In FIG. 17(c), each sensor structure 4 a, 4 b has two vertical Hallelements and two Horizontal Hall elements. Such a sensor structure canfor example be used to determine an angular position when used inconjunction with a dipole ring or disk magnet, and when mounted in anoff-axis position or in a through-shaft position (e.g. as described inpatent application EP19193068.4 and/or EP20191167.4).

FIG. 17(d) shows a variant of FIG. 17(a), which can be used incombination with a two-pole ring or disk magnet when mounted in anoff-axis position or in a through-shaft position.

FIG. 17(e) shows a variant of FIG. 17(b), which can be used incombination with a two-pole ring or disk magnet when mounted in anoff-axis position or in a through-shaft position.

FIG. 17(f) shows a variant of FIG. 17(c), which can be used incombination with a two-pole ring or disk magnet when mounted in anoff-axis position or in a through-shaft position.

It is explicitly pointed out that the present invention is not limitedto these particular sensor structures. They are chosen merely toillustrate that the sensor elements of the first and secondsemiconductor dies need not be exactly located on top of each other, andmay even contain integrated magnetic concentrators (IMC) if the uppersemiconductor substrate has a thickness of at least 100 micron, or atleast 150 micron, or at least 200 micron. From the above, it should beclear to the skilled person that other sensor structures can also beused, for example sensor structures with magneto-resistive elements (notshown).

FIG. 15 , FIG. 16 and FIG. 17 shows embodiments where the first andsecond sensor structure 4 a, 4 b of the first and second semiconductorsubstrate are identical. That is however not required for the presentinvention to work. It suffices that the two semiconductor dies have thesame size and shape, and that the two sensor structures have the sameoffset dx, dy from the geometric center in order for the magneticcenters L1, L2 to coincide when stacked and rotated and offset (e.g.shifted) as described in FIG. 7 to FIG. 11 . As an example, FIG. 18shows a stacked die arrangement with two semiconductor dies 1802 a, 1802b having different magnetic sensor structures 1804 a, 1804 b, configuredfor measuring the angular position of the respective semiconductor dies.

The present invention has been explained so far for rectangularsemiconductor dies which are not square, which are rotated by 180°relative to each other, and offset (e.g. shifted) relative to eachother. However, the present invention is not limited thereto, and willalso work for two semiconductor dies having a square or rectangularshape, and having a sensor structure offset from its geometrical center,which are stacked, and rotated by another angle, for example 90°, oreven an angle smaller than 90°, and optionally offset or shifted.

FIG. 19(a) shows a square semiconductor die 1902 having a sensorstructure 1904 (schematically indicated by a square) which is offset bya distance “dx” in the X-direction from the geometric center 1906 of thesemiconductor die 1902, in top view. In this example, the semiconductordies have bond pads adjacent only one edge, and the shift over “dx” isin a direction parallel to the edge adjacent the bond pads 1907.

FIG. 19(b) shows a stack of two semiconductor dies shown in FIG. 19(a)in top view, after rotating the upper die 1902 b by 90° with respect tothe lower die 1902 a, and after shifting the upper die in de X-directionby DX equal to dx, and in the Y-direction by DY equal to dx, so as toalign the sensor structures 1904 a, 1904 b (schematically indicated by asquare). As can be seen, the plurality of bond pads of bothsemiconductor dies are exposed for easy electrical connection to thelead frame (not shown), e.g. by wire-bonding.

In a variant of FIG. 19 , the semiconductor die has bond pads along twoof its edges (for example similar as in FIG. 21 ).

FIG. 20(a) shows a rectangular semiconductor die 2002 having a sensorstructure 2004 (schematically indicated by a square) which is offset bya distance “dx” in the X-direction from the geometric center 2006 of thedie 2002, in top view. In this example, the semiconductor dies have bondpads adjacent only one edge, and the shift over “dx” is in a directionparallel to the edge adjacent the bond pads.

FIG. 20(b) shows a stack of two semiconductor dies shown in FIG. 20(a)in top view, after rotating the upper die 2002 b by 90° with respect tothe lower die 2002 a, and after shifting the upper die 2002 b in deX-direction by DX, and in the Y-direction by DY, so as to align theirsensor structures 2004 (schematically indicated by a square). As can beseen, the plurality of bond pads of both semiconductor dies are exposedfor easy electrical connection to the lead frame (not shown), e.g. bywire-bonding.

FIG. 21(a) shows a semiconductor die 2102 which is a variant of thesemiconductor die 2002 shown in FIG. 20(a), in that it has bond padsalong two of its edges.

FIG. 21(b) shows a stacked die assembly which is a variant of thestacked die assembly of FIG. 20(b). As can be seen, the bond pads areexposed at the top side of the semiconductor dies and can easily beelectrically connected to the lead frame, e.g. using wire-bonding.

FIG. 22(a) shows a rectangular semiconductor die 2202 having a sensorstructure 2204 (schematically indicated by a square) which is offset bya distance “dx” in the length direction X and by a distance “dy” in thewidth direction Y from the geometric center 2206 of the semiconductordie 2202, in top view. This is a variant of FIG. 20(a) where the sensorstructure 2204 is shifted in 2 directions. In this example, thesemiconductor die has bond pads near only one edge.

FIG. 22(b) shows a stack of two semiconductor dies shown in FIG. 22(a)in top view, after rotating the upper die 2202 b by 90° with respect tothe lower die 2202 a, and optionally after shifting the upper die 2202 bin de X-direction by DX and in the Y-direction by DY, so as to aligntheir sensor structures 2204 (schematically indicated by a square). Ascan be seen, the plurality of bond pads of both semiconductor dies areexposed for easy electrical connection to the lead frame (not shown),e.g. by wire-bonding.

In a variant (not shown) of FIG. 22(a) and FIG. 22(b), the semiconductordies have bond pads located adjacent two of its edges, for example,similar as shown in FIG. 21(a) and FIG. 22(b).

FIG. 23(a) shows a stack of two square semiconductor dies 2302 a, 2302 bin top view, each die having a sensor structure 2304 which is located ata position near one of its corners. In the example, the dies are stackedafter rotating the upper die over about 15° about an axis normal to thesemiconductor dies and passing through the magnetic centers, but otherangles can also be used, for examples angles in the range from about 10°to about 85°, or from 15° to 80°, or from 15° to 40°. As can be seen,the plurality of bond pads of both semiconductor dies are exposed foreasy electrical connection to the lead frame (not shown), e.g. bywire-bonding. The skilled person having the benefit of the presentdisclosure can easily find a suitable angle, for example by trial anderror.

FIG. 24 shows a stack of two square semiconductor dies 2402 a, 2402 b intop view, each die having a respective sensor structure 2404 a, 2404 bwhich is offset from its geometrical center 2406 a, 2406 b byapproximately 25% of the width W of the die. The dies are stacked afterrotating the upper die over about 15° about an axis normal to thesemiconductor dies and passing through the magnetic centers. As can beseen, the plurality of bond pads of both semiconductor dies are exposedfor easy electrical connection to the lead frame (not shown), e.g. bywire-bonding. The skilled person having the benefit of the presentdisclosure can easily find a suitable angle, for example by trial anderror.

For completeness, it is noted that the sensor structure cannot beshifted in just any direction. The following table provides a list ofshifts that work:

TABLE 1 List of shifts sensor location #pad shift versus geometricalcase zones of dies rotation center of die Example A 1 DY only 180° shift away from pad FIG. 7-9 zone, at least ZZ/2 in Y-direction B 2 DXand 180°  shift away from pad FIG. 10-11 DY zones, at least ZZ/2 in eachdirection C 1 DX and 90° shift parallel or away FIG. 19, 20, DY from padzone, at least 22 ZZ D 2 DX and 90° shift parallel or away FIG. 21 DYfrom both pad zones, at least ZZ E 1 20°-90° minimum angle is FIG. 23,24 function of dxwhere ZZ is the width of the zone containing the bond pads.

The invention claimed is:
 1. A sensor device comprising: a lead frame; afirst semiconductor die having a first rectangular shape with a firstgeometrical center, and being electrically connected to the lead frame,and comprising a first sensor structure situated at a first sensorlocation; a second semiconductor die having a second rectangular shapeequal to the first rectangular shape, and having a second geometricalcenter, and being electrically connected to the lead frame, andcomprising a second sensor structure situated at a second sensorlocation; wherein: the first rectangular shape has a length defining alength direction, and a width defining a width direction perpendicularto the length direction, said length being equal to or larger than saidwidth; the first sensor location is offset from the first geometricalcenter by a first predetermined offset along the length direction, andby a second predetermined offset in the width direction; at least one ofthe first and second predetermined offset is different from zero; thesecond sensor location is offset from the second geometrical center; thesecond semiconductor die is stacked on top of the first semiconductordie, and is rotated by 180° with respect to the first semiconductor dieabout an imaginary axis perpendicular to the lead frame; and the secondsemiconductor die is shifted in the first direction by a first distanceequal to twice the first predetermined offset and shifted in the seconddirection by a second distance equal to twice the second predeterminedoffset.
 2. The sensor device according to claim 1, wherein the firstsemiconductor die comprises a plurality of first bond pads wire-bondedto the lead frame; and wherein the second semiconductor die comprises aplurality of second bond pads wire-bonded to the lead frame; wherein thefirst wire bonds and the second wire bonds are situated on a same sideof the lead frame.
 3. The sensor device according to claim 1, whereinthe relative position of the first sensor location with respect to thefirst rectangular shape is identical to the relative position of thesecond sensor location with respect to the second semiconductor die. 4.The sensor device according to claim 1, wherein the second semiconductordie has a layout identical to that of the first semiconductor die. 5.The sensor device according to claim 1, wherein one of the first andsecond predetermined offset is equal to zero, and the other of the firstand second predetermined offset is different from zero.
 6. The sensordevice according to claim 1, wherein each of the first and secondpredetermined offset is different from zero.
 7. The sensor deviceaccording to claim 1, wherein each of said first and secondsemiconductor die has an active side and a passive side, and wherein theactive side of the first semiconductor die is oriented in the samedirection as the active side of the second semiconductor die.
 8. Thesensor device according to claim 1, wherein the second semiconductor dieis stacked on top of the first semiconductor die, without a spacer orinterposer.
 9. The sensor device according to claim 1, wherein the firstsensor structure on the first semiconductor die is identical to thesecond sensor structure on the second semiconductor die.
 10. The sensordevice according to claim 1, wherein the first sensor structure on thefirst semiconductor die is different from the second sensor structure onthe second semiconductor die.
 11. The sensor device according to claim1, wherein the first sensor structure and the second sensor structureare magnetic sensor structures.
 12. The sensor device according to claim1, wherein the first semiconductor die is situated between the secondsemiconductor die and the lead frame.
 13. The sensor device according toclaim 1, wherein the sensor device comprises only two semiconductordies, namely said first semiconductor die and said second semiconductordie.
 14. The sensor device according to claim 1, wherein the firstsemiconductor die and the second semiconductor die overlap by at least60%.
 15. The sensor device according to claim 11, wherein each of thefirst and second semiconductor die is configured for providing a linearor an angular position based on magnetic field gradients.
 16. A sensorsystem comprising: a magnetic sensor device according to claim 11; and amagnetic source arranged in the vicinity of the magnetic sensor device.17. The sensor system according to claim 16, wherein said magneticsource comprises at least one permanent magnet.
 18. A sensor devicecomprising: a lead frame; a first semiconductor die having a firstrectangular shape with a first geometrical center, and beingelectrically connected to the lead frame, and comprising a first sensorstructure situated at a first sensor location; a second semiconductordie having a second rectangular shape equal to the first rectangularshape, and having a second geometrical center, and being electricallyconnected to the lead frame, and comprising a second sensor structuresituated at a second sensor location; wherein: the first rectangularshape has a length defining a length direction, and a width defining awidth direction perpendicular to the length direction, said length beingequal to or larger than said width; the first sensor location is offsetfrom the first geometrical center by a first predetermined offset alongthe length direction, and by a second predetermined offset in the widthdirection; at least one of the first and second predetermined offset isdifferent from zero; the second sensor location is offset from thesecond geometrical center; and the second semiconductor die is stackedon top of the first semiconductor die, and is rotated by 90° withrespect to the first semiconductor die about an imaginary axisperpendicular to the lead frame.
 19. The sensor device according toclaim 18, wherein one of the first and second predetermined offset isequal to zero, and the other of the first and second predeterminedoffset is different from zero.
 20. The sensor device according to claim18, wherein each of the first and second predetermined offset isdifferent from zero.
 21. The sensor device according to claim 18,wherein the first semiconductor die and the second semiconductor dieoverlap by at least 60%.
 22. The sensor device according to claim 18,wherein the first semiconductor die comprises a plurality of first bondpads wire-bonded to the lead frame; and wherein the second semiconductordie comprises a plurality of second bond pads wire-bonded to the leadframe; and wherein the first wire bonds and the second wire bonds aresituated on a same side of the lead frame.
 23. A sensor devicecomprising: a lead frame; a first semiconductor die having a firstrectangular shape with a first geometrical center, and beingelectrically connected to the lead frame, and comprising a first sensorstructure situated at a first sensor location; a second semiconductordie having a second rectangular shape equal to the first rectangularshape, and having a second geometrical center, and being electricallyconnected to the lead frame, and comprising a second sensor structuresituated at a second sensor location; wherein: the first sensor locationis offset from the first geometrical center; the second sensor locationis offset from the second geometrical center; and the secondsemiconductor die is stacked on top of the first semiconductor die, andis rotated by an angle in a range from 10° to 85° with respect to thefirst semiconductor die about an imaginary axis perpendicular to thelead frame.
 24. The sensor device according to claim 23, wherein one ofthe first and second predetermined offset is equal to zero, and theother of the first and second predetermined offset is different fromzero.
 25. The sensor device according to claim 23, wherein each of thefirst and second predetermined offset is different from zero.
 26. Thesensor device according to claim 23, wherein the first semiconductor dieand the second semiconductor die overlap by at least 60%.
 27. The sensordevice according to claim 23, wherein the first semiconductor diecomprises a plurality of first bond pads wire-bonded to the lead frame;and wherein the second semiconductor die comprises a plurality of secondbond pads wire-bonded to the lead frame; and wherein the first wirebonds and the second wire bonds are situated on a same side of the leadframe.